1. Field of the Invention
The invention herein relates to fluid dispensing devices in which a generated gas pressure causes discharge of fluid contained in the device over an extended period of time.
2. Description of the Prior art
Discharge of fluids from containers over extended periods of time is a necessity in many fields. For instance, many medications must be administered to patients in small, incremental doses over time, either continually or intermittently. Similarly, many chemical and biological processes and tests conducted in laboratories require prolonged infusion of reactants in small amounts over the course of the process or test. To meet this need, many devices have been introduced to the market which provide for intermittent or continual dispensing of liquid medications, reactants, and so forth. To dispense the liquids, some devices have included miniature electric liquid pumps, others have included miniature gas pressure generators, and some have relied on initial high gas pressure within the device. Among the devices which have been described or used have been those described in my prior U.S. Pat. Nos. 4,402,817; 4,522,698; 4,687,423; 4,886,514; 4,902,278; 5,038,821; 5,149,413; 5,788,682; 5,928,194 and 5,938,640.
Such prior devices have operated essentially on an xe2x80x9csteady statexe2x80x9d mode, so that if they are operating they are normally dispensing the liquid at what is intended to be a constant rate. However, in many operational situations the flow from the device becomes blocked or restricted, at least for part of the time, or needs to be varied according to internal or external parameters of the device or its environment. For instance, variations in back pressure from the target environment (such as intravenous or intraarterial pressure in a patient) will affect the flow rate of the dispensing device. In the past such changes in flow rate could only be compensated for by adjustment of a device manually, normally based on observation of the device""s operation by the user or operator. Requiring manual correction or compensation of a device""s operation is of course undesirable, because it is time consuming and requires constant or frequent attendance by the user or operator, and because in many cases changes in flow rate, particularly small ones, may not be observable by a user or operator until the cumulative effect of such small changes has become significant and perhaps harmful.
The present invention is of a fluid dispensing device which includes both a gas pressure generating device and an internal feedback system which allows the device to make changes in its own operation to respond in a timely and measured manner to changes, even small ones, in the dispensing flow rate of the fluid contained in the device. The feedback system operates effectively even under conditions where the cause of restriction or expansion of flow rate is not unequivocally known or reasonably capable of direct measurement.
The device of this invention comprises a fluid reservoir which has a fluid outlet which optionally may have a pressure or flow resistance unit incorporated into the outlet. It also has an electric gas generation module which generates a driving gas, preferably by electrochemical means, to provide gas pressure to force the contained fluid out of the reservoir through the outlet (and resistance unit, if present) to the target environment. The reservoir is divided into separate but adjoining chambers for the generated driving gas and for the fluid (liquid, vapor or gas) to be dispensed. The chambers are separated by a moveable fluid-tight partition, against which the gas pressure on one chamber is exerted, and which in response to such gas pressure, moves to force the fluid in the other chamber from the reservoir and out through a outlet, commonly a fluid conduit such as rigid or flexible tubing or a gas vent such as a grille.
Also present is a sensor for detecting and measuring a variable parameter which may be internal or external to the device, but which is related directly or inversely to the operation of the device and the discharge or dispensing of the fluid. Such a parameter may be physical, chemical or biological, such as, for instance, fluid pressure or volume within either chamber of the reservoir, discharge fluid flow rate or discharge fluid exit pressure, or concentration of a component of the fluid. The sensor sends a signal defining the rate, direction and/or magnitude of any change in that parameter to a controller which controls the electric current which operates the gas generation module. The quantity and rate of gas generation are thereby regulated by the controller""s variation of the current operating the gas generation module, which in turn varies the gas pressure within the reservoir and thus the flow rate and quantity of the fluid which is dispensed, such dispensing thus being responsive to changes in the measured parameter.
The controller operates in response to signals from the sensor of changes in the measured parameter to control the electric current flow in a manner which causes the gas generation module to increase or decrease the module""s gas generation rate so as to maintain fluid dispensing flow rate within prescribed limits.
Because the device therefore maintains substantial constant flow rate based on response to a specific internal or external parameter which is in some manner indicative of the fluid dispensing rate of the device, its control and operation are not dependent on detection or measurement of highly variable or difficultly measured system or target properties which are or may be the source of the change in the measured parameter. For instance, flow of fluid from a hypodermic syringe into a patient""s artery or vein will be impeded or speeded up by changes in the patient""s intraarterial or intravenous blood pressure. These pressures are difficult or cumbersome to detect and measure, but their effect on the fluid dispensing flow results in an increase or decrease in the gas pressure in the reservoir required to move the fluid against the intraarterial or intravenous pressure. Such gas pressure within the reservoir, in contrast, can be easily detected and measured by a sensor, when then can initiate the operations described above to adjust the electric current and gas generation rate to compensate for the variations in the intraarterial or intravenous pressure, notwithstanding that the latter have not been directly measured.
The fluid to be dispensed may be a liquid, such as a liquid medication, a vapor such as a scented vapor for indoor air freshening or a medicinal vapor such as for use as an inhalant by patients with breathing difficulties, or a gas such as an inhalant or a chemically reactive gas which is being dispensed for use in a chemical or biological process.
Therefore, in one embodiment the invention involves a fluid dispensing device comprising a housing having an internal fluid reservoir divided by a movable fluid-tight partition into first and second chambers on opposite sides of the partition; electrically operated gas generation module for generating gas and moving the gas into the first chamber and exerting pressure on the partition; liquid outlet means from the second chamber for dispensing of fluid contained in the second chamber under pressure from contact with the partition; sensor means for detection and measurement of an operational parameter of the device over time and generation of a signal indicating quantity and direction of any change in the parameter, such change in the parameter resulting in change to flow rate of liquid from the second chamber; and controller means responsive to the signal for adjusting electrical current to the module in a manner which will change gas pressure within the reservoir, whereby change in gas pressure induced by the current change is in a direction and amount sufficient to keep the liquid flow rate at any time from exceeding predetermined minimum and maximum values for the parameter.
In another embodiment, the invention involves a fluid dispensing device comprising a housing having an internal fluid chamber comprising a gas compartment and a liquid compartment separated by a moveable pressure responsive member, the liquid compartment having a restricted liquid outlet conduit providing liquid communication between the liquid compartment and an outlet end of the conduit, the outlet end opening to an exterior of the housing; pumping means comprising an electrochemical cell in gas communication with the gas compartment, for pumping gas into the gas compartment , which gas exerts pressure against the pressure responsive member causing responsive movement thereof into the liquid compartment, thereby causing liquid within the liquid compartment to move toward and through the liquid outlet conduit to the exterior of the housing; a pressure sensor for measurement of gas pressure in the gas compartment; detection means for determining liquid flow rate at the outlet end of the liquid outlet conduit; and current control means responsive to gas pressure measurement of the pressure sensor and liquid flow rate determination for adjusting of electrical current in the cell; whereby upon change in gas pressure or environmental temperature which results in change of the liquid flow rate at the outlet end of the liquid outlet conduit causes the current control means for adjusting the electrical current in the cell to increase or decrease the current and increase or decease the pumping of gas into the gas compartment, to return the liquid flow rate to a value pertaining immediately prior to the change in gas pressure or environmental temperature, such that over an operating period of the device fluid flow rate of the liquid being discharged through the outlet end of the liquid outlet conduit remains substantially constant.
In yet another embodiment, the invention involves a method of controlling fluid discharge rate from a fluid dispensing device which comprises providing a fluid dispensing device comprising a housing having an internal fluid chamber comprising a gas compartment and a liquid compartment separated by a moveable pressure responsive member, the liquid compartment having a restricted liquid outlet conduit providing liquid communication between the liquid compartment and an outlet end of the conduit, the outlet end opening to an exterior of the housing, and pumping means comprising an electrochemical cell in gas communication with the gas compartment, for pumping gas into the gas compartment, which gas exerts pressure against the pressure responsive member causing responsive movement thereof into the liquid compartment, thereby causing liquid within the liquid compartment to move toward and through the liquid outlet conduit to the exterior of the housing; measuring gas pressure in the gas compartment; determining liquid flow rate at the outlet end of the liquid outlet conduit; and in response to measured value of the gas pressure measurement and liquid flow rate, determining whether change in gas pressure or environmental temperature has occurred resulting in change of the liquid flow rate at the outlet end of the liquid outlet conduit, and thereupon increasing or decreasing electrical current in the cell, thereby respectively increasing or deceasing the pumping of gas into the gas compartment, as required to return the liquid flow rate to a value pertaining immediately prior to the change in gas pressure or environmental temperature, such that over an operating period of the device fluid flow rate of the liquid being discharged through the outlet end of the liquid outlet conduit remains substantially constant.
Other embodiments and aspects of the invention will be evident from the description below.